A fixing device includes a fixing belt, a pressurizing roller, and a heating member. The pressurizing roller comes into press-contact with the fixing belt to form a nip. The heating member heats a sheet between the fixing belt and the pressurizing roller. The heating member includes a heating heater and a holding member that holds the heating heater.
A surface on the nip side of the heating member is sometimes formed in a curved convex shape. With this structure, the pressurizing roller presses the fixing belt in a bent state. Therefore, the pressurizing roller can equalize pressure in the nip in the axial direction of the fixing belt.
Since the surface on the nip side of the heating member is the curved convex shape, bending stress is generated if the heating member is pressed by the pressurizing roller. The bending stress decreases if the pressing by the pressurizing roller is released. Since the pressurization and the depressurization of the heating member by the pressurizing roller are repeated, the bending stress repeats an increase and a decrease. Therefore, durability of the heating member deteriorates over time.